One-step synthesis of FA 1-x GA x PbI 3 perovskites thin film with enhanced stability of alpha (α) phase

In this work, formamidinium lead iodide (FAPbI 3 ) with different Guanidinium (GA) content (2.5%, 5%, 10% and 20%) were successfully deposited by a spin coating method. The influence of GA incorporation into the FA 1-x GA x PbI 3 films was studied. The crystal structures, surface morphology and optical properties have been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), photoluminescence and UV–Visible spectrometer, respectively. The crystalline structure of the undesirable δ and desirable α-phase were found in the orientation of (010) and (110) planes at diffraction angles 2 θ = 11.5° and 13.8°, respectively. It is observed from the XRD results that the GA content plays an important role in the formation of α/δ phases and stabilization of the α-FAPbI 3 phase. Herein, the 10% GA is an adequate amount for FA 1-x GA x PbI 3 lead to a homogenous, stable α-phase, rough surface, large in grain size and formation of pinhole-free perovskite film. The optical analysis revealed that by increasing the GA content decrease the band gape to lower energy from 1.75 to 1.41 eV. Furthermore, after 15 days the stability of 10% GA was found that remained excellent in a ~60% humid environment. The obtained results indicated that the incorporation of GA into FAPbI 3 films makes it promising candidates for photovoltaic application.